The present invention relates to a pellicle for protecting the pattern surface of a reticle used for exposure patterning when manufacturing semiconductor devices such as LSIs (Large Scale Integrated circuits), and a case for accommodating the pellicle.
When performing exposure patterning in the manufacture of semiconductor devices such as LSIs, a semiconductor substrate is irradiated with a laser beam by using a reticle formed with a pattern as a mask. Accordingly, the patterning precision often depends on the precision of a pattern formed on the reticle (to be referred to as a reticle pattern hereinafter).
If a foreign substance such as dust attaches to the pattern-formed surface of the reticle (to be referred to as a reticle pattern surface hereinafter), a pattern image formed on the semiconductor substrate deforms from a predetermined one. In order to prevent this inconvenience, a pellicle for foreign substance attachment prevention is formed on the reticle pattern surface. This pellicle is comprised of a pellicle frame having a desired height so as to surround the reticle pattern surface, and a membrane-like pellicle film bonded to the upper end face of the pellicle frame to be almost parallel to the pattern surface of the reticle. In the following description, the pellicle is regarded as an assembly including the reticle.
When exposure patterning is performed by using the pellicle, the pellicle is irradiated with a laser beam. Hence, a plurality of deposition control materials which contribute to formation of deposits on the reticle pattern surface cause chemical reaction, or a deposition control material which promotes formation of deposits on the reticle pattern surface attaches to the pattern surface.
For example, sometimes ammonia or ammonium ions existing in the atmosphere react with sulfuric acid or sulfate ions remaining on the reticle pattern surface to deposit ammonium sulfate on the reticle pattern surface. Sulfuric acid or sulfate ions originating from a sulfuric acid-based cleaning agent used in the manufacturing process, particularly the cleaning step as the final step, of the reticle often remain on the reticle surface. The remaining sulfuric acid or sulfate ions are assumed to promote deposition reaction upon laser beam irradiation.
Conventionally, Japanese Patent Laid-Open Nos. 3-166545 and 9-68793 propose to apply a pressure-sensitive adhesive agent to the inner surface of a pellicle frame so a foreign substance will not attach to the reticle pattern surface. However, the foreign substance discussed in these references is not a deposition control material as described above but dust and the like. This deposition control material is difficult to capture with only the pressure-sensitive adhesive agent, and formation of deposits on the reticle pattern surface cannot be sufficiently prevented.
Therefore, in order to suppress deposition of a foreign substance on the reticle pattern surface, countermeasures such as use of a pellicle material that does not produce ammonia, reduction of residual sulfuric acid on the reticle pattern surface, and reduction of gases leaking from a pellicle case have been employed. With these countermeasures alone, however, it is difficult to sufficiently prevent formation of deposits on the reticle pattern surface, since ammonia and the like are always present in an ordinary environment and tend to be thick in the pellicle.